1. Field of the Invention
The present invention relates generally to the field of air filter devices. More particularly, filter devices structured for coupling with a breathing apparatus, such as a respirator or mask or other source of suction, and so as to provide multiple filter elements functioning as a single filtering unit.
2. Description of the Related Art
When a person is subject to adverse breathing conditions, such as in an environment contaminated with airborne particles and/or harmful vapors, that person""s safety and health will require some type of device for filtering the air before it passes into his or her lungs. To achieve this goal, requirements for such filtering devices have been codified (42 C.F.R. xc2xa784) by the National Institute of Occupational Safety and Health (NIOSH). NIOSH regulations were revised to be made substantially more stringent (in June 1995, with a grandfather clause for three years, effective June 1998), to require that these filtering devices demonstrate increased efficiency, a measure of its ability to remove contaminants from air as it is drawn (breathed) through the filtering device.
Historically, improvements in the efficiency of a filtering device have resulted in a concomitant increase in the difference in air pressure between the environment and the interior of the filtering device required for drawing air through it at a given rate. This pressure differential is commonly referred to as pressure drop of the filtering device. Further, increased efficiency in a filtering device also typically has led to a reduction in the effective life span of the filtering device. Consequently, with prior art filtering devices, greater safety through improved filter efficiency has typically made such devices difficult to breathe through and of extremely limited life span. As a result, in addition to breathing discomforts, users experience frequent periods of down time as they must either leave the work area and/or stop working to remove and replace filtering devices.
Accordingly, it has long been a goal of those in the field of filtering devices to develop a filtering device that meets the natural and codified safety requirements of users while demonstrating a pressure drop that is sufficiently low to allow comfortable breathing by the user and, even more importantly, while A functioning effectively for a greater period of time.
To attain such improvements, inventors have manipulated the shapes and sizes of the air filters to maximize surface area in the hope that, with increased area over which filtering can be conducted, acceptable efficiency can be realized while at the same time affording the user a low pressure drop and, thus, comfortable breathing. However, filters can be made only so large before they begin to interfere with a user""s vision or mobility. Inventors have also experimented with improved materials in attempted furtherance of the same goals. To date, even slight improvements in efficiency, pressure drop, or life span have been hailed as marked improvements in the art.
One attempt to increase the surface area of the filter is illustrated in U.S. Pat. No. 2,130,555 to Malcolm. The Malcolm patent shows a dust filter unit of a generally tubular form, but having within the unit a filter having a plurality of bellows-like folds. The bellows-like folds provide increased surface area in the filter without the necessity of increasing the diameter of the unit.
The filter unit shown by Malcolm has the advantage of increasing the surface area of the filter medium. However, the folds are part of an integrally formed filter media. Therefore, the design does not permit more or less surface area to be used in accordance with particular needs.
U.S. Pat. No. 2,227,959 to Cover shows a filter composed of three elements connected to one another. The three elements are each structured differently from one another so as to be placed at an assigned position in the filter. However, the device requires specialized innermost and outermost filter elements, which would require that at least three types of filter units be kept in stock at all times. Further the construction of the filter shown in Cover, in which the filter walls are tucked into a cavity in a retaining plate, would be somewhat prone to leakage, compared to modern units in which the filter walls are sealingly engaged to one another around their periphery, and might not meet the more stringent standards in effect today, such as those promulgated by NIOSH.
U.S. Pat. No. 2,235,624 to Schwartz shows a filter unit for respirators having a cylindrical filter casing of a depth sufficient to hold two disk-shaped filter pads. The filter pad within the casing farthest away from the breathing mask is formed of two circular pads stitched together circumferentially at the edges to form the disk-shaped filter pad, and having an aperture formed through both circular pads to allow a supporting tube element to pass there through. The disk-shaped filter pad closest to the mask is formed similarly but is only apertured on one side. The supporting tube enters the aperture of this innermost pad and comes to an end therein without passing entirely through the innermost pad.
The filter unit taught by Schwartz has several disadvantages. For one thing, the requirement of rigidity of the outer cylindrical filter holder would tend to increase the weight of the mask. Also, since the depth of the filter holder is set, only a set number of the disk-shaped filter pads may be used. Moreover the innermost filter pad is of a different construction than the outermost pad, which means that, similar to the situation in the Cover patent, two types of replacement filter elements must be maintained in stock.
U.S. Pat. No. 2,951,551 to West shows an air purifying cannister that is formed from individual filtration units fitted together. Each unit has a male as well as a female connector and a rigid outer wall. The units may be mated in series ad infinitum to form a composite cannister of desired length. Each unit has a tube formed therethrough to allow for the passage of already-filtered air from one unit to the next. The tube is fitted with a cap on the unit farthest from the mask or source of suction to prevent unfiltered air from entering the tube.
The West filter unit, due to the requirement for rigidity, would become very heavy and would be very uncomfortable for the wearer after prolonged use, especially in comparison to the light-weight simple disk filter pad units currently preferred for long term use. Further the weight of the cannister, as additional units are added, would cause a great deal of stress to be applied to the air inlet of any mask using the filter, which may lead to fatigue of the connection materials and eventual breakage.
A common disadvantage of the types of filter units described above is the high ratio of non-functioning structural materials to functioning filtration material. As a result of this ratio, providing the user with increased filter surface area would result in an associated increase in weight of the filter. Modern filter units are expected to be light in weight, to ensure the comfort of the user.
A prevalent type of light-weight filter pad currently in use is the 3M(copyright) P100 Particulate filter, which consists of a single light-weight disk-shaped unit, formed of two fabric filter pads affixed to one another around the circumference of each pad. One of the filter pads has a central aperture being supported around its periphery by a plastic fastener integrally formed with a bayonet-style female connector, formed to enable a locking connection with a counterpart male connector at the input or inputs of a breathing mask.
However, while the 3M(copyright) P100 filter pad offers the advantage of light weight, due to its construction it can function only as a single unit. Further, because the pad is soft, installation and removal of the filter pad exerts torsional and crushing stress on the filter material as the user grips and twists the filter to engage or disengage the connector that mates with the mask.
Thus, in view of the above deficiencies of the prior art devices, the need exists for a filter unit that is of very light weight but which can be stacked to any level of stacking so as to customize the filter depending upon the use and the environment. There also is a need for such a stackable filter in which each stackable unit thereof is of identical construction. Further, there is a need for a filter structured to permit installation and removal without the application of possibly damaging stresses to the filter fibers.
One of the very commonly experienced problems in using presently available breath protection equipment, is the difference in the level of protection and breathing comfort experienced from the start of a fresh set of filtering units, and the level of protection and breathing comfort towards or at the end of the expected life cycle (end of life,) of these filter units. Most of these filters and filter units do not have an xe2x80x9cend of lifexe2x80x9d indicator. This leaves it up to the user to estimate the life remaining in a filter, which may result in serious breathing discomfort, and sometimes a lack of protection. All of this can lead to the wearer""s exhaustion, injury and damage to his or her health, and the resulting loss of productivity. As a result, wearers of these filter devices often end up discarding them long before the end of the expected life span, thereby increasing the cost of protection.
In addition to the problems discussed above, an end user of a filter device has to go through a series of trials and errors before determining the optimum fit for the device, such as a mask, to which the filters are connected. In carrying out this trial and error process, the end user could damage a number of filter devices. Further, if the end user""s hands are contaminated, as is usually the case, he would need the help of another individual with clean hands. This would limit the usability of these filter devices, drive up the cost of their use because of the higher number of labor hours required, and may lead to or exacerbate problems and inconveniences, such as language problems, difficulty in achieving the optimum fit, interpersonal relations between the user and helper, and so on.
Another difficulty faced by users of filtration devices is the requirement that a xe2x80x9cfit checkxe2x80x9d be performed. Fit check is a method by which the wearer blocks the air inlet(s)xe2x80x94where the filter device(s) would fit into and be attached to the respirator or mask, and takes a deep inhaling breath, thereby creating a vacuum inside the respirator or mask. If the respirator or mask properly fits around the face of the wearer, he should feel this vacuum, and not feel any air leakage around the periphery of the mask where it contacts his face.
Because of the increased awareness of environmental safety, and in view of the increase in the use of toxic and other materials dangerous to health in the industrial processes, fit check has come to be seen as an important requirement for effective usage of these sophisticated breathing protection devices. That is, if the breathing protection device does not fit/seal properly around the face of the wearer, all the advances in the filtering devices will be to little avail. However, filter pads such as the 3M(copyright) P100 do not allow a fit check to performed while the filter is connected to the mask.
In light of the foregoing, it becomes clear that a filtering device furthering the seemingly incompatible goal of improving efficiency while decreasing pressure drop and increasing the effective life span of the filtering device, and additionally providing a means for performing fit check while the filter is attached to the mask, would represent a significant advance over the prior art.
In view of the above-mentioned problems of prior art devices, and the needs and concerns of users of filtration devices, it is an object of the present invention to provide a filtering device that demonstrates improved efficiency while exhibiting reduced pressure drop, an extended usable life span, and ideally is structured to facilitate the use of the fit check method. It is a further object of this invention to provide the end user with the ability to customize the number of filter elements or devices on his or her respirator mask, or such other apparatus, to provide an optimum combination of protection, breathing comfort and cost for the situation at hand. With this ability, the user may combine old/used filter unit or units with new/fresh filter unit or units, thereby allowing him to achieve a customized level of comfort to carry on his job where breathing protection is required.
It is another object of the present invention to provide each individual wearer the ability to design fit the total filter to his own comfort level, and at the same time maintain breathing comfort throughout his work period. In addition, it is an object of the present invention to provide safety to the user even when using a filter device beyond its safe level.
It is another object of the present invention to make it possible to keep very low levels of inventory of filters and filter devices, while providing adequate supply at the same time, by providing identical, stackable filtration units.
It is yet another object of the present invention to provide a means for connecting and disconnecting the filter device from a mask or additional filter unit without applying stress to delicate filter material.
Additional objects and advantages of the present invention will become clear in view of the detailed description and the accompanying diagrams.
In furtherance of the above and other objects, there is provided a stackable filter device for filtering an input to a source of suction. The device comprises: a substantially hollow filter pad having first and second filter walls constructed of a filter material, the periphery of the first filter wall being sealingly engaged to the periphery of the second filter wall to form the filter pad, each of the filter walls having an aperture. The first and second filter walls each have an annular member fixedly contacted to the circumferential edge of the aperture. The annular members support the aperture, and are structured so as to integrally form connectors operable to removably connect the filter device to the source of suction or to an additional filter device on a first side of the filter device and to a sealing end cap or an additional filter device on a second side of the filter device. The filter device preferably includes a tubular stiffening member passing through the filter device. The stiffening member is rigidly attached at each end thereof to one of the annular members. The stiffening member comprises a perforated tubular shaft forming an air passage through the filter device.